Medical device position location systems, devices and methods

ABSTRACT

Methods, devices and systems for three-dimensional location of the disposition of a sensor coil in a subject including are disclosed. The systems include an array of three or more quadruplet drive coil sets, where each quadruplet drive coil set include at least four discrete drive coils, at least one moveable sensor coil configured to provide one or more sensor coil response signals, a first system component providing AC drive signals to energize the discrete drive coils, a second system component for receiving the one or more sensor coil response signals from the at least one moveable sensor coil, and a processor configured to determine a sensor coil disposition of the at least one moveable sensor coil in the subject relative to the quadruplet drive coil sets based on the one or more sensor coil response signals.

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority to U.S. Provisional Patent ApplicationNo. 62/119,092, filed on Feb. 20, 2015, the entire disclosure of whichis incorporated herein by reference.

TECHNICAL FIELD

This disclosure generally relates to locating the position of a medicaldevice within a patient, and more particularly relates to locating theposition of a medical device within a patient using electromagneticfield and electrocardiograph responses.

BACKGROUND

In medical care, the correct placement of a medical device such as acatheter or a guide wire in a patient has become increasingly importantfor a number of reasons. In the case of an infusion catheter, for oneexample, medications may need to be targeted to or for specific organsor areas of the body. In some instances, it may be important to place acatheter sufficiently near the heart where a particular blood flow rateensures adequate dilution and mixing of infused fluids. Alternatively, acatheter or other internally-positioned medical device may simply needto be disposed in the right place to function; as for example, anenteral feeding tube within the stomach. Use of a medical deviceposition location and/or guidance system may thus provide for skilledand less skilled practitioners to more simply and/or accurately andreliably position a medical device such as a catheter and in someinstances without the use of an x-ray or additional ancillary proceduresto confirm the location of the catheter or device. Additionally, the useof a medical device position location system additionally may providefor maintenance of the sterile field, a critical aspect in placingcatheters or other internally positioned medical devices.

Accordingly, a variety of systems have been developed to attempt toindicate location or position of catheters or other medical devicesdisposed within the body of a patient. Relatively reliable locationdevices have made use of x-ray or fluoroscopy; however, these devicesmay expose the patient and/or caregiver to undesirable amounts ofradiation. As a consequence, a variety of different systems have beenattempted to more continuously and accurately indicate location of acatheter or other medical device with a goal of reducing and/orreplacing the use of x-rays and as an alternative to fluoroscopy.However, such systems thus far developed still suffer from variousdrawbacks.

Electromagnetic catheter position location devices have been the subjectof research and development. Some such locating systems have used an ACdriven coil in the catheter tip with external sensor coils. Adisadvantage of such a conventional catheter tip driven system has beenthe need for heavy or thick wires running into the catheter to carrynecessary drive current to generate a sufficient electromagnetic signalfor external sensors. This has precluded the use of such a system withsmaller diameter catheters or other such smaller medical devices. Otherposition location systems have used a fixed magnet (or DC) on a cathetertip with external sensor coils. A significant disadvantage to such afixed magnet location system has been that the magnet would necessarilybe very small, and as such would generate a very small signal from thetip of the catheter. Additionally, DC magnet systems put an additionalcharge into the patient and as a consequence, other magnetic fields inthe vicinity may create significant interference problems for such asystem. Furthermore, the field of such a magnet drops off extremelyquickly over distance and thus cannot be sensed more than a few inchesdeep into the patient's tissue. This results in some concern about thedepth of the placement in the subject.

Some locating systems have made use of AC driven external coils and asensor coil in the catheter tip. One such AC drive system has beendescribed including driving two coils simultaneously; however, thoserespective coils were specified as having been driven at two differentfrequencies so that the coil drives are not additive and the sensordemodulates the two different frequencies as two independent values. Yetanother AC drive system has been described driving two coilssimultaneously in quadrature which simulates a single spinning coil;however, this system may only indicate the orientation of the sensor inthe x-y plane and its relative position in that plane.

This statement of background is for information purposes only and is notintended to be a complete or exhaustive explication of all potentiallyrelevant background art.

SUMMARY

Briefly summarized, devices, methods and systems of thepresently-disclosed subject matter are directed to devices and/ormethods configured for accurately determining position and/or locationof a sensor coil within a subject by using a moveable sensor coil. Thissensor coil communicatively operates with, or responds to an array ofdrive coil sets of drive coils placed relative to a subject's body toallow detection and/or determining of positioning of the medical devicein the subject's body. Each of the drive coil sets and the sensor coilmay also be communicatively connected to or cooperative with one or morecomponents which may include an external control and/or display whetherin one or more boxes, the one or more components providing for one ormore of respective selective driving of the drive coils of the sets ofdrive coils and/or for receiving response signals from the sensor coil.A determining component may also or alternatively also be included todetermine medical device position using the response signals.

Methods, devices and systems may be provided for one or both of two- orthree-dimensional location of the disposition of a sensor coil in asubject including: an array of electromagnetic drive coil sets, each sethaving two or three dimensionally oriented drive coils; a sensor coilbeing electromagnetically communicative with the array ofelectromagnetic drive coil sets; and, typically, a system controller orone or more like components communicative with and adapted to energizeone or more of the electromagnetic coils in the array of electromagneticdrive coil sets, the energizing of the one or more of theelectromagnetic coils including one or more of energizing the coilssingly, or in pairs of x-y, and y-z, or x-z coils while measuring theresponse of the sensor coil; whereby a system hereof may then use themeasurements of the responses of the sensor coil to calculate one orboth of the location and orientation of the sensor coil relative to saiddrive coil sets.

The improved methods and systems for electro-magnetic tip location ofpatient catheters or other internally disposed medical devices describedherein may be particularly useful for determining a more accurate z-axislocation. The determination of the z-axis location allows for one orboth more accuracy and certainty regarding the final placement of thecatheter or medical device. An alternative embodiment incorporating adigital signal processor and alternative methodology, in some instancesimplemented in software architecture, may be used to determine that adetermined and specified axis signal is approaching a null measuredvalue. The sensor coil provides this response to the determiningcomponent of the system. The signal may then be estimated usinginformation from the measured axes. For example, if the z-axis isapproaching a sensed null value, the methodology is configured to usex-axis signal (x vector sum) and the measured y-axis signal (y vectorsum) to calculate and substitute a position vector for the z-axissignal. The methodology may be operable to make the calculation andsubstitution when the measured response from the z-axis falls below aselected threshold. In turn, this provides a novel approach to using atriplet and/or quadruplet structure to determine the position in threedimensions of the sensor coil.

These and still further aspects and advantages of the present subjectmatter are illustrative of those which may be achieved by thesedevelopments and are not intended to be exhaustive or limiting of thepossible advantages which may be realized. Thus, these and other aspectsand advantages of these present developments will be apparent from thedescription herein or may be learned from practicing the disclosurehereof, both as embodied herein and/or as modified in view of anyvariations that may be apparent to those skilled in the art. Thus, inaddition to the exemplary aspects and embodiments described herein,further aspects and embodiments will become apparent by reference to andby study of the following description, including as will be readilydiscerned from the following detailed description of exemplaryimplementations hereof especially when read in conjunction with theaccompanying drawings in which like parts bear like numerals throughoutthe several views.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a schematic overview of an exemplar of some presentdevelopments hereof.

FIG. 2 is a detailed view of one three-axis drive coil set.

FIG. 3 is a plan view of one three-axis drive coil set.

FIG. 4 is a detailed view of one four-axis drive coil set.

FIG. 5 is an exploded view of one embodiment of a four-axis drive coilset, including the patient drive coil block.

FIG. 6 is a view of one embodiment of a four-axis drive coil set,including the patient drive coil block

FIG. 7 is a detailed view of a sensor coil.

FIG. 8 is a detailed view of one embodiment of connection for the sensorcoil to the determining component.

FIG. 9 is an illustration of magnetic vectors generated by a normaltriplet coil drive.

FIG. 10 is an illustration of orthogonal magnetic vectors generated byan x-y virtual drive.

FIG. 11 is an illustration of orthogonal magnetic vectors generated by ay-z virtual drive.

FIG. 12 is an illustration of magnetic vectors generated by a normaltriplet coil drive.

FIG. 13 is an illustration of magnetic vectors generated by a quadrupletdrive coil.

FIG. 14 is an illustration of magnetic vectors generated by a quadrupletdrive coil.

FIG. 15 is an illustration of orthogonal magnetic vectors generated by aquadruplet drive coil arrangement.

FIG. 16 is a schematic overview of a present development hereof.

FIG. 17 is a schematic overview of another present development hereof.

FIG. 18 is a schematic overview of yet another present developmenthereof in which the present development is placed on a subject.

FIG. 19 is a schematic block diagram of a present development hereof.

FIG. 20 is a schematic block diagram of a present development hereof.

FIG. 21 is a further schematic block diagram of an exemplardisplay/interface and user control box as may be used herein.

FIG. 22 is still a further schematic block diagram of a main interfaceboard in a user control box as may be used herein.

FIG. 23 is yet one further schematic block diagram of a patient drivecoil block as may be used herein.

FIG. 24 is still yet one further schematic block diagram of a patientdrive coil block connected to a 12 drive coil array as may be usedherein.

FIG. 25a-25g are methodologies for controlling an acquisition of sensorcoil position.

FIG. 26 is a schematic block diagram of a coil drive with virtual x-ycapability.

FIG. 27 is a schematic block diagram of a coil drive with virtual x-ycapability.

FIG. 28 is a schematic block diagram of sensor coil signal processing.

FIG. 29 is a schematic block diagram of a coil drive with full virtualx-y-z capability.

FIG. 30a-30b are methodology alternatives for controlling one or boththe acquisition and display of sensor coil position in virtual x-y-zsystem.

FIG. 31 is a schematic block diagram of a coil drive with full virtualx-y-z′-z″ capability.

DETAILED DESCRIPTION

FIG. 1 provides an overview of an implementation of a medical deviceposition location system 100 hereof. Shown in FIG. 1 are schematicrepresentations of some alternative possible parts including a usercontrol box 102 (which may be or include one or more components foroperation of the other parts), and a patient drive coil block 122 withdrive coil set 106, representative of any sets 106 a, 106 b, 106 c, aguide wire or stylet with a sensor coil 114 and cable 118 (or othercommunication medium), and optional ECG connections 112, 116. A usercontrol box 102 may be included though it might more appropriately bedefined by the components thereof, a component for driving coils and asecond component for receiving response signals, and/or optionally adetermining component for determining position from the responsesignals. These components may be in or define an otherwise “black” box102, or may otherwise be disparately disposed and merely operativelyconnected to each other by hard wires or wirelessly, or mayalternatively be substantially physically indiscriminate one or morefrom each other though nevertheless operatively configured to achieveone or more of the driving, receiving and/or determining elements.

Schematically shown in FIG. 1, these components may be in and/or definethe schematic box 102. Furthermore, a control box 102 whether of a blackbox nature or physically disposed may include other operative parts, andaccording to this implementation shown in FIG. 1, may contain a displaysuch as a touch screen display 104, a single-board computer (SBC) (notseparately shown in FIG. 1) for control and data processing, and/or amain interface board (also not separately shown in FIG. 1) which mayconnect to a drive block cable 108 and a medical device cable or member118 (also sometimes referred to as a catheter, or guide wire or styletcable 118). A patient drive coil block 122 may be connected via driveblock cable 108 to the control box 102 (the drive coil block alsosometimes being referred to as an emitter block, a patient block ormerely a drive block). Coil drive electronics 110 and three drive coilsets 106 a, 106 b, 106 c (also sometimes referred to as emitter coils,or x-y-z drive coils, or x-y-z′, and z″) are mounted in the drive block122. The coil drive electronics 110 allow the SBC to selectivelyenergize any drive coil axis 126, 128, 124 of a set 106 (see FIG. 2) orgroup of drive coil axes. A sensor coil 114 is, in this implementation,built on or within the tip of a medical device such as a small diameterbiocompatible guide wire or stylet cable 118. The guide wire may then beplaced in the patient and the catheter then threaded over this wire; or,alternatively, the stylet cable may then be inserted up to the distalend of a catheter before the catheter is placed in the patient. Atwo-conductor cable 120 may be used to connect the sensor coil of guidewire or stylet back to the user control box. In this embodiment, an ECGmain cable 116 connects the ECG signal input receiver 112 to thecircuitry associated with the drive block 122 or the coil driveelectronics 110.

FIG. 2 shows a detailed drawing of a drive coil set 106 (representativeof any of sets 106 a, 106 b, 106 c). Here, the x-coil 124, the y-coil126 and z-coil 128 each have a ferrite or ferrous core 130 to enhancethe magnetic field generation. In an alternative embodiment, the coils,124, 126, 128 each have an air core or no core material. This figure isonly schematically representative of the construction of a drive coil;in actuality, each drive coil may have many windings (e.g. 100 turns) onthe ferrite core and may be constructed as three (3) coil pairs tofacilitate the intersection of the x, y, and z axes. Each coil here hasa set of lead wires 132 to connect back to the multiplexers of the coildrive electronics 110.

FIG. 3 shows a plan view of a triplet drive coil set 106. In thisrepresentation the x-coil 124 and the y-coil 126 and the z-coil 128 aredisposed relative to each other in an orthogonal arrangement. Each coilhere has a set of lead wires 132 to connect back to the multiplexers ofthe coil drive electronics 110.

FIG. 4 shows a detailed drawing of an alternative quadruplet drive coilset 106 (representative of any sets 106 a, 106 b, 106 c). Here, thex-coil 124, the y-coil 126, and the z′-coil 134, and z″-coil 136 (theselatter two also referred to as the “z-coils”) each have a ferrite orferrous core 130 to enhance the magnetic field generation. Additionally,to further enhance the magnetic field generation z′-coil 134 and z″-coil136 are arranged orthogonally in relation to each other, butnon-orthogonally in relation to the x-coil 124 or y-coil 126. In thisrepresentation, the z′-coil 134 and the z″-coil 136 are orientedforty-five degrees off the standard arrangement of a z-axis, in astandard x-y-z coil array, also referred to as “off-axis”. Alternativelydescribed, the respective z-coils may be arranged in perpendicular toeach other and geometrically oriented off axis at both a negative 45degree angle and positive 45 degree angle away from the respective x, yaxis. In such an arrangement, wherein the x-coil and y-coil are arrangedorthogonally relative to each other and at least two other z-coils arearranged orthogonally relative to each other but the z-coils are“off-axis” or non-orthogonal relative to the x-coil and y-coil, thesystem is referenced as pseudo-orthogonal or in some instances as duallyorthogonal. Where four drive coils are contained in one set the set isreferred to as a quadruplet.

FIG. 5 shows an exploded two-dimensional schematic drawing of aquadruplet drive coil set. Here, the x-coil 124, the y-coil 126, and thez′-coil 134, and z″-coil 136 each may have a ferrite or ferrous core 130to enhance the magnetic field generation. Additionally, to furtherenhance the magnetic field generation z′-coil 134 and z″-coil 136 arearranged orthogonally in relation to each other, but non-orthogonally inrelation to the x-coil 124 or y-coil 126. In this representation, thez′-coil 134 and the z″-coil 136 are oriented forty-five degrees off thestandard arrangement of a z-axis, in a standard x-y-z coil array. Insome embodiments, the drive coil electronics 110 (circuit board)separates the z′-coil 134 and z″-coil 136 in to two distinct segmentsboth above and below the imaginary plane created by the x-coil andy-coil arrangement. Optionally an additional aspect of this embodimentincludes, at least one capacitor 131 operably associated with the drivecoil to create an LC circuit.

FIG. 6 shows an three-dimensional schematic drawing of a quadrupletdrive coil set. Here, the x-coil 124, the y-coil 126, and the z′-coil134, and z″-coil 136 each may have an air core 133 to enhance themagnetic field generation. Additionally, to further enhance the magneticfield generation z′-coil 134 and z″-coil 136 are arranged orthogonallyin relation to each other, but non-orthogonally in relation to thex-coil 124 or y-coil 126. In this representation, the z′-coil 134 andthe z″-coil 136 are oriented forty-five degrees off the standardarrangement of a z-axis, in a standard x-y-z coil array. In someembodiments, the drive coil electronics 110 (circuit board) separatesthe z′-coil 134 and z″-coil 136 in to two distinct segments both aboveand below the imaginary plane created by the x-coil and y-coilarrangement. Optionally, at least one capacitor 131 is operablyassociated with the drive coil to create an LC circuit for theinductance, energizing, or driving of the electromagnetic coils.

FIG. 7 shows a detailed view of an exemplar medical device; e.g., aguide wire or stylet sensor coil. The sensor coil 114 may be anysuitable gauge (e.g., but not limited to, a very fine gauge (e.g. 0.001″diameter)) wire wound around a ferrous core wire 138. In some instances,the sensor coil 114 and sensor coil lead wires may be insulated. In someembodiments the core wire 138 is composed of an alloy that affects anumber of functional characteristics of the sensor coil (e.g.flexibility, semi-permeable magnetic properties, and conductivity). Thisfigure is schematically illustrative only of the sensor coil; here, thesensor coil is approximately 400 turns in single layer, but may be anysuitable turns per length, e.g., 50-1000, or any range or value therein,e.g., 100, 200, 300, 350, 400, 450, 500, 550, 600, 650, 700, and thelike. The sensor coil lead wires 142 connect back through a cable to thepatient isolated portion of the main interface board. An electricalinsulator 140 may be used to provide a protective sleeve and/or coatingfor the assembly. An alternative construction may optionally include twoor more sensor coils wrapped around the ferrous core wire 138. Anadditional sensor coil would likely need additional lead wires toconnect back to the patient isolated portion of the main interfaceboard. In an optional ECG version of a catheter location system, the tipof the ferrous, conductive core wire 138 may be polished smooth and mayremain uncoated and/or unsheathed and may provide an electrical signalas an ECG lead from within the catheter.

In an alternative representation, the ECG version of the sensor coillocation system (e.g., FIG. 8) the conductive core wire 138 is operablyconnected to an electrical connector or jack 144 (in this alternativeembodiment the connection component may be a 3.5 mm female stereo plug148, in one example) which may provide the output and signal to thepatient isolated portion of the main interface board. In such a version,the guide wire or stylet sensor connection may be accomplished withthree wires, two (2) for the coil sensor and one (1) for the ECG,through a cable 146 to the patient isolated portion of the maininterface board in the user control box 102 (not separately shown inFIG. 8).

FIGS. 9, 10 and 11 illustrate an optional version of the operation of atriplet normal-drive and virtual-drive drive coil set. FIG. 9 showsmagnetic vectors x, y, and z generated by normal coil 149 driving of thex-axis coil 124, the y-axis coil 126 and z-axis coil 128 (as shown inFIG. 2). FIG. 10 shows the virtual magnetic vector x-y 151 generated bysimultaneously driving the x-axis coil 124 and the y-axis coil 126 (asshown in FIG. 2) and when both are driven at the same power, the vectoris forty-five degrees between the x and y axes. The virtual magneticvector x-(−y) generated by simultaneously driving the x-axis coil 124and the phase-inverted, y-axis coil 126 (as shown in FIG. 2) and whenboth are driven at the same power, the vector is minus forty-fivedegrees between the x and -y axes. If a digital to analog converter(DAC) is added to control power to the x-axis drive and another DACadded to control power of y-axis drive, then it is possible to point thevirtual axis to any angle from 0 to 360 degrees between x and y. Forexample, if x-axis power DAC is maximum and y-axis power DAC is ¼^(th)(one quarter) of maximum then the vector sum of x-y drive yields avirtual axis of approximately fourteen degrees between the x and y axes.FIG. 11 shows a virtual magnetic vector y-z 153 generated bysimultaneously driving the z-axis coil 124 and the y-axis coil 126 (asshown in FIG. 2); and a virtual magnetic vector z-(−y) generated bysimultaneously driving the z-axis coil 124 and a phase-inverted, y-axiscoil 126 (as shown in FIG. 2). These figures illustrate the simplest andone optional form of virtual drive (e.g., see FIG. 25), it is possibleto point a virtual magnet vector to any polar coordinate bysimultaneously driving x, y, and z coils at independent power levels(e.g., see FIG. 29).

FIGS. 12, 13, 14, and 15 illustrate an optional version of the operationof a quadruplet normal-drive and virtual-drive drive coil set. FIG. 12shows magnetic vectors x, y, and z generated by normal coil 149 drivingof the x-axis coil 124, the y-axis coil 126 and z-axis coil 128 (asshown in FIG. 2; FIG. 12 provides a reference for the orientation of thepseudo-orthogonal orientation of z′-axis and z″-axis). FIG. 13 shows thex, y, z′ and z″ magnetic vectors 155 and shows what would be the virtualz vector formed from the z′ and z″ magnetic vectors. It is noted thatrelative powering of the z′-coil and z″-coil may be used to generate avirtual z vector as depicted in FIG. 13, but also other virtual magneticvectors from the x, y, z′, and z″ normal-drive coils. FIG. 14 shows thediscrete x, y, z′ and z″ magnetic vectors 157 super-imposed on thequadruplet coil set such as those shown in FIGS. 4, 5, and 6. FIG. 15shows the four virtual magnetic vectors of x-y and z′-z″ 159 generatedby simultaneously driving the x-axis coil 124 and the y-axis coil 126(as shown in FIG. 2) and by simultaneously driving the z′ and z″ axiscoils. In this alternative and when both x-axis and y-axis are driven atthe same power, the vector is forty-five degrees between the x and yaxes. The virtual magnetic vector x-(−y) generated by simultaneouslydriving the x-axis coil 124 and the phase-inverted, y-axis coil 126 (asshown in FIG. 2) and when both are driven at the same power, the vectoris minus forty-five degrees between the x and -y axes. If a digital toanalog converter (DAC) is added to control power to the x-axis drive andanother DAC added to control power of y-axis drive, then it is possibleto point the virtual axis to any angle from 0 to 360 degrees between xand y. For example, if x-axis power DAC is maximum and y-axis power DACis ¼^(th) (one quarter) of maximum then the vector sum of x-y driveyields a virtual axis of approximately fourteen degrees between the xand y axes. FIG. 15 further shows a virtual magnetic vector z′-z″generated by simultaneously driving the z′-axis coil 134 and the z″-axiscoil 136 (as shown in FIG. 4); and a virtual magnetic vector z′-(−z″)generated by simultaneously driving the z′-axis coil 134 and aphase-inverted, z″-axis coil 136 (as shown in FIG. 2). These figuresillustrate the simplest and one optional form of virtual drive (e.g.,see FIG. 26), it is possible to point a virtual magnet vector to anypolar coordinate by simultaneously driving x, y, and z coils or in somecases z′-coil and z″-coil at independent power levels (e.g., see FIG.31).

Furthermore, FIG. 16 provides a schematic diagram of a medical deviceposition location system with an optional electrocardiograph (ECG)measurement. This is similar to the FIG. 1 implementation with theaddition of three ECG leads. The user control box 102 connects through amain interface board 158 to the drive block cable 108 and guide wire orstylet cable 146. The patient drive block 122 may be connected via driveblock cable 108. Three isolated ECG leads 152 communicate signals to thecontrol box 102. The coil drive electronics 110 and three x-y-z drivecoil sets 106 a, 106 b, 106 c may be mounted in the drive block 122. Thecoil drive electronics 110 allow the single board controller 166 (SBC)to selectively energize any drive coil axis 126, 128, 124 (FIG. 2) orgroup of drive coil axes. In this embodiment, three ECG pads 154 may beplaced on the patient and connected by ECG lead wires 152 to an ECGsignal input receiver 112 that connects an ECG main cable 116 to thedrive block 122. These two, three, or more ECG inputs together with theone ECG from the catheter may provide at least a three-lead ECGmeasurement system (e.g., see FIGS. 23 and 24). The guide wire or styletsensor 114 here is built onto a small diameter biocompatibleconductive-tip guide wire or stylet cable 146 which is inserted into acatheter before (stylet) or after (guide wire) the catheter is placed inthe patient. A drive block cable 108 connects the patient drive coilblock 122 to the user control box 102. In alternative embodiments, theuser control box houses the main interface board 158, the single boardcontroller 166, and in some instances isolates the power supplyconnections. In some embodiments (not shown in the figures), the ECGsignal input receiver 112 may be operably housed, contained, and/orconnected to either the drive block 122 or the user control box 102.Moreover, in alternative embodiments, the ECG pads 154 may connectwirelessly to at least one or more selected from the group of: the ECGsignal input receiver 112, the driver block 122, or the user control box102. In these embodiments, the ECG measurement may be displayed on theuser control box 102 and a touch screen 104 may be used in associationwith a graphical user interface adapted to display the location of thesensor coil 114 in relation to the patient drive block 122 over time. Insome embodiments, the ECG measurement may be displayed solely on thetouch screen display 104. In alternative non-limiting embodiments, theECG measurement may be displayed simultaneously with the location of thesensor coil 114. In yet another non-limiting embodiment, the sensor coillocation and orientation may be displayed on the display 104, withoutadditional information related to the ECG measurement data.

FIG. 17 provides a schematic diagram of a medical device positionlocation system with an optional electrocardiograph (ECG) measurementwherein the drive coil array contains 12 drive coils arranged andoriented as depicted in FIGS. 13, 14 and 15. The user control box 102connects through a main interface board to the drive block cable 108 andguide wire or stylet cable 146. The patient drive block 122 may beconnected via drive block cable 108. Three isolated ECG leads 152communicate signals to the control box 102. The coil drive electronics110 and three x-y-z drive coil sets 106 a, 106 b, 106 c may be mountedin the drive block 122. The coil drive electronics 110 allow the singleboard controller (SBC) to selectively energize any drive coil axis 126,124, 134, 136 (FIG. 4) or group of drive coil axes. Two, or three ormore ECG pads 154 may be placed on the patient and connected by ECG leadwires 152 to the drive block 122. The guide wire or sensor coil 114 hereis built onto a small diameter biocompatible conductive-tip guide wireor stylet cable 146 which is inserted into a catheter before (stylet) orafter (guide wire) the catheter is placed in the patient. A drive blockcable 108 connects the guide wire or stylet sensor coil and optionallyone ECG lead back to the user control box 102. FIG. 17 shows the patientdrive coil block 122 may have two or more ECG pads added which connectthrough a cable 152 to the patient isolated portion of the maininterface board. These two, three, or more ECG inputs may together withthe one ECG from the catheter provide at least a three-lead ECGmeasurement system.

FIG. 18 is an overall schematic diagram of a medical device positionlocation system in use relative to a subject or patient. This figureillustrates connections between a user control box 102 and a sensingguide wire or stylet 114 and a patient drive block 122. The control box102 may include an integrated, separated, or remote user display and/orinterface. Each of these components may include cables or connectors orwireless communications for one or more of a coil interface, a powersupply, a serial interface, a control interface, a status interface, anECG interface or lead, an oscillator interface, a processor interface, acomputer interface, a data interface, a network interface (cable orwireless), an internet interface, a video interface, a touch-screeninterface, an SBC control or power interface, a board interface, asensor interface, an isolator interface, and/or the like as describedherein or as known in the art. One or more of these cables or connectorsmay attach to the patient drive block 122 or any component thereof. Thisfigure further demonstrates one possible insertion point 160 into thesubject. Optionally, in this instance the device may be inserted in aperipheral vasculature of the subject, specifically the right arm of thepatient. Optionally, the system may be configured for use at otherinsertion sites on the patient's body as may be determined by eithermedical staff and/or the desired application and use of the system.Additionally, FIG. 18 shows placement of this embodiment of the patientdrive block where the designated drive block notch 162 is aligned withor near the sternal notch of the subject 164. In alternativeembodiments, the system could optionally be implemented for use among anumber of different entry or insertion points (e.g. peripheral insertion(cephalic vein), midline insertion (basilic vein), central venousinsertion (interjugular vein), chest insertion (subclavian vein oraxillary vein) or groin (femoral vein)). Moreover, in yet anotherimplementation, the system could be used for placement at insertionsites for nephrostomy or kidney dialysis. The patient drive block 122may be adapted to different shapes, configurations, or arrangements thatmay align with anatomical features of the subject. In alternativenon-limiting embodiments, the designated drive block notch may beadapted to be one or more of a notch, an extrusion, a marked portion, oran alignment hole. These embodiments may assist in the medical personnelplacing the patient drive block on the subject aligned with anatomicalfeatures of the subject.

FIG. 19 provides a schematic diagram of a medical device positionlocation system wherein the drive coil array contains 12 drive coils. Inthis embodiment, optional ECG measurement components may be disconnectedfrom the system entirely or not included in the patient drive block 150.In this non-limiting approach the coils are arranged and oriented asdepicted in FIGS. 13, 14 and 15. The user control box 102 connectsthrough a main interface board to the drive block cable 108 and guidewire or stylet cable 146. The patient drive block 150 may be connectedvia drive block cable 108. The coil drive electronics 110 and threex-y-z drive coil sets 106 a, 106 b, 106 c may be mounted in the driveblock 150. In this embodiment, the patient drive block 150 may notinclude two or more ECG leads with patient isolation. The coil driveelectronics 110 allow the single board controller (SBC) to selectivelyenergize any drive coil axis 126, 124, 134, 136 (FIG. 4) or group ofdrive coil axes. The guide wire or sensor coil 114 here is built onto asmall diameter biocompatible conductive-tip guide wire or stylet cable146 which is inserted into a catheter before (stylet) or after (guidewire) the catheter is placed in the patient. A drive block cable 108connects the guide wire or stylet sensor coil to the user control box102. It should be noted that, FIG. 16 shows an alternative embodimentwherein the patient drive coil block 122 may have two or more ECG padsadded which connect through a cable 152 to the patient isolated portionof the main interface board. FIG. 19, is provided to show that thesystem 100 may be adapted to use a patient drive block 122 or a patientdrive block 150, the patient drive block 150 being a non-limiting aspectnot adapted to provide ECG measurements.

FIG. 20 is another schematic diagram of a medical device positionlocation system. This figure illustrates connections between a usercontrol box 102 (again, box 102 may be merely a schematic “black” box ormay be physically disposed, the one or more components thereof includingone or more of a first component for driving the coils, a secondcomponent for receiving signals and a determining component fordetermining location; noting also that the one or more components may bephysically disparate from each other and merely operatively connected,or may alternatively be substantially physically indiscriminate one ormore from each other though nevertheless operatively configured toachieve one or more of the driving, receiving, measuring, and/ordetermining elements) and a sensing guide wire or stylet 114 and apatient drive block 122, 150. The control box 102 may include anintegrated, separated, or remote user display and/or interface. Each ofthese components may include cables or connectors or wireless for one ormore of a coil interface, a power supply, a serial interface, a controlinterface, a status interface, an optional ECG interface or lead, anoscillator interface, a processor interface, a computer interface, adata interface, a network interface (cable or wireless), an internetinterface, a video interface, a touch-screen interface, an SBC controlor power interface, a board interface, a sensor interface, an isolatorinterface, and/or the like as described herein or as known in the art.One or more of these cables or connectors or wireless may operativelyattach to the patient drive block 122 or any component thereof. In thisembodiment the power connection is isolated as further depicted in FIG.22. Note, the power, serial control and status and ECG may be optional;i.e., these may be part hereof or discrete functionalities; whereascomponents, whether in or disparate from a box 102 (black box orotherwise) for driving coil operation, receiving sensor coil signals,and/or determining location would be preferred, though again, these maybe together physically, perhaps indiscriminately, or may be disparatephysically and merely operatively connected as needed or desired.

FIG. 21 is a block diagram of an exemplar user control box 102 which inthis implementation may include a computer 166, which in a number ofexamples may include a digital signal processor (aka DSP), a display104, optionally either or both LCD with or without touch-screencapabilities, and a main interface board 158. Each of these componentsmay include cables or connectors or wireless for one or more of a coilinterface, a power supply, a serial interface, a control interface, astatus interface, an optional ECG interface or lead, an oscillatorinterface, a processor interface, a computer interface, a datainterface, a network interface (cable or wireless), an internetinterface, a video interface, a touch-screen interface, a computercontrol or power interface, a board interface, a sensor interface, anisolator interface, a digital signal processor, a zero insertion force(ZIF) socket, and/or the like as described herein or as known in theart.

FIG. 22 provides a block diagram of a main interface board 158 (FIG.20), associated circuitry, and shows a patient isolated section whichconnects to a guide wire or stylet cable 120 and optional ECG leads froma patient drive block 122. The remainder of the circuitry controlspower/interface to a patient drive block 122 and power to a single boardcomputer 156, which may include one or more of a voltage regulator, awatchdog switch, a drive switch, a power isolator, a voltage monitor, acable buffer, a filter, an analog to digital converter, a digital signalprocessor, a demodulator clock, a phase adjuster, a demodulator, asignal filter, a programmable gain amplifier, a coil isolator, a coilsensor coil amplifier, a detector, memory, flash memory, a multiplexor,a polarity inversion switch, and/or the like. Each of these componentsmay include cables or connectors or wireless for one or more of a coilinterface, a power supply, a serial interface, a control interface, astatus interface, an optional ECG interface or lead, an oscillatorinterface, a processor interface, a computer interface, a datainterface, a network interface (cable or wireless), an internetinterface, a video interface, a touch-screen interface, an SBC controlor power interface, a board interface, a sensor interface, and/or thelike as described herein or as known in the art. One or more of thesecables or connectors or wireless may attach to a patient drive block 122or any component thereof. In this representation, the circuitry isoperably configured to have a power isolation circuit and a single boardcomputer status and control isolation circuit which span the patientisolation line. Additionally, this representation demonstrates theintegration of a programmable digital signal processor, which amongother functions, may be configured to furnish the appropriate AC drivesignal to the patient drive block and control the phase of the signalprovided to a demodulator clock.

FIG. 23 is a block diagram of a patient drive block 122 (FIGS. 1, 16,17, 18, 19, 20). An alternative version/option of a patient drive block122 has two or more ECG leads connected. The drive coil drive system inthis diagram illustrates a two-coil virtual drive capability allowingthe first component for driving coil operation (which may include or beconfigured with methodologies whether in computer software or otherwise)to simultaneously drive two or more coils at select power levels. Such asystem may include one or more of a voltage regulator, a watchdogswitch, a drive switch, a power isolator, a voltage monitor, a cablebuffer, a filter, an analog to digital converter, a phase adjuster, ademodulator, a signal filter, a programmable gain amplifier, a coilisolator, a coil sensor coil amplifier, a detector, memory, flashmemory, a multiplexor, a polarity inversion switch, and/or the like.Each of these components may include cables or connectors or wirelessfor one or more of a coil interface, a power supply, a serial interface,a control interface, a status interface, an optional ECG interface orlead, an oscillator interface, a processor interface, a computerinterface, a data interface, a network interface (cable or wireless), aninternet interface, a video interface, a touchscreen interface, an SBCcontrol or power interface, a board interface, a sensor interface,and/or the like as described herein or as known in the art.

FIG. 24 provides a block diagram of the patient drive block circuitry asin FIG. 21; however, shows the optional connection to a 12 drive coilarray (FIG. 16, inter alia). In alternative embodiments, the drive coilarray may have numerous drive coils capable of functioning for theintended purpose (e.g. some embodiments possess 15, 18, 21, 24 or moredrive coil arrays). The drive coil arrays are disposed as optionally setout in FIGS. 13, 14, 15 and 17, inter alia, and additional arrangementsand configurations are contemplated by the addition of additional drivecoil arrays. In alternatives (not depicted in the Figures), the drivecoil arrays may be arranged orthogonally or pseudo-orthogonally asdescribed in FIGS. 13-15, but not limited to those implementations.

FIGS. 25a-g provide an overview by flow charts of methodologyfunctionality options for a medical device position location systemhereof. FIG. 25a provides an initial check sub-process. FIGS. 25b and25c provide alternatives for operation, including energizing coils andreading of coil responses; FIG. 25b for a 9-coil array (x, y, z), andFIG. 25c for a 12-coil array (x, y, z′, z″). FIG. 25d providessubsequent steps including particularly optional ECG data acquisitionand evaluation. FIG. 25e and FIG. 25f provide some alternativesubsequent steps for a determining component to use sensor coil responsesignals to determine sensor coil position and/or location. FIG. 25gprovides some optional display steps and a finish or loop back to thestart.

FIG. 26 is a simplified real and virtual coil drive system located on apatient drive block 122, 150. A coil driver hereof may have only twocoil drives and only high/low power selection instead of a power controlDAC. In this drive system it is possible to generate x-y and x-(−y)virtual coil drive (see FIG. 10) and also y-z and y-(−z) drive (see FIG.11). One additional feature of this drive is a low power setting whichallows drive power reduction if the sensor coil is too close to thedrive coil (see methodology flow chart FIG. 25e ). It also is possibleto have two additional virtual vectors in this drive system by drivingx-high-power together with y-low-power or driving x-low-power withy-high-power. Here, driving x-low-power together with y-low-power yieldsthe same virtual axis—forty-five degrees from x and y axes—as drivingboth at high power. Optionally, this system may be extended to use forand with the x-z and y-z virtual drives and/or virtual driveimplementations of z′ and z″ coils.

FIG. 27 is a simplified real and virtual coil drive system located on apatient drive coil block 122 wherein the coil array includes a 12 drivecoil array inclusive of the z′-coil and the z″-coil.

FIG. 28 is a schematic view of what may be a determining component in abroad sense, and in this implementation is a sensor coil processingsystem of the main interface board 156 as it uses the electromagneticsignal 168 received by the sensor coil 114. The sensor coil 114 on theguide wire or stylet may be connected through a cable 120, 146 orwirelessly to the main interface board 156. The first system componentwhich may include a programmable digital signal processor (DSP)providing the drive signals to the coils on the patient drive blockand/or controlling the oscillation of the drive coils (theelectromagnetic emissions) and the coil clock. The first systemcomponent with or without a DSP controls and in some implementationsselects a preferred low frequency electromagnetic wavelength at whichthe drive coil array 106 will be driven to oscillate. This sensor coil114 receives the electromagnetic waves as input which is communicatedto/received by the second system component. These are sensor coilresponse signals. These response signals may be pre-amplified andfiltered then optionally passed through a patient isolation transformerto a gain amplifier which may be a software-controlled programmable gainamplifier. This amplified signal is then demodulated using the lowfrequency (e.g. 16 kHz) drive oscillator. Concurrently, the DSP may beused to provide oscillator input signals and phase control signals to ademodulator clock. The demodulator clock signals may pass to asynchronous demodulator. The synchronous demodulator and associatedsoftware then reads the sensor coil value with a high resolution (e.g.16 bit or higher resolution) analog to digital converter (ADC). Thisread value is for each drive coil activation and this value isproportional to the magnetic field measured by the sensor coil duringthat drive coil activation.

FIG. 29 is a schematic view of an optional more complex virtual drivesystem. This drive system allows the x-axis coil set 170, the y-axiscoil set 172 and z-axis coil set 174 to all be driven simultaneously atindependent power levels set by computer control through individualdigital to analog converters (DAC). In this drive system, the virtualmagnetic vector is the vector sum of x-axis drive plus y-axis drive plusz-axis drive. This virtual drive permits the virtual vector to point toany polar coordinate in space, and thus use polar coordinates as anoption; however, it may often still be preferable to use a set of threeorthogonal “virtual” axes to calculate the sensor coil 114 position.This alternative further demonstrates a possible integration of thedigital signal with a complex drive system.

FIGS. 30a-b provide a methodology flow chart showing optional changesfor drive and sensor coil response processing for a fully independentx-y-z virtual drive system (see FIG. 29). This methodology may add apositive offset test and a negative offset test to the virtual axes forthe A-corner set of coils. If the sensor coil response is stronger foran offset axis (FIG. 30b ) than the current virtual axes, the systemshifts to use the offset axes.

FIG. 31 is a detailed view of yet another non-limiting embodiment of amore complex virtual drive system. This drive system allows the x-axiscoil set 170, the y-axis coil set 172, z′-axis coil set 176, and z″-axiscoil set 178 to all be driven simultaneously at independent power levelsset by a controller (which may include or involve a computer control)through individual digital to analog converters (DAC). In this drivesystem, the virtual magnetic vector is the vector sum of x-axis driveplus y-axis drive plus z-axis drive. In this instance, the z-axis drivemay be obtained using measured values from the z′-axis drive and thez″-axis drive. This virtual drive permits the virtual vector to point toany polar coordinate in space, and thus use polar coordinates as anoption; however, it may often still be preferable to use a set of threeorthogonal “virtual” axes to calculate the sensor coil 114 position.This alternative further demonstrates an integration of the digitalsignal with a complex drive system.

A feature of the present developments may include providing an accuratesystem to generate a three-dimensional indication of one or more oflocation, position, orientation, and/or travel of a medical device suchas a guide wire, catheter, or stylet placed within a patient. A systemhereof may include a sensor coil which is disposed in or on the tip of aguide wire or stylet cable, this sensor coil being communicativelyoperative and cooperative with one or more components for driving coils,receiving responses and/or determining position; these components beingin or defining in some implementations an external control and/ordisplay box which may also be communicatively connected with an array ofthree-axis, four-axis, or a multiple array of axes drive coils. This,may in some implementations, include a display of the location and/ortravel of the device. The array of drive coils are placed in someimplementations in a triangular block on the patient's chest. This isalso sometimes referred to as a drive block, an emitter block, orpatient drive block. In some embodiments, the location and travel may bedisplayed in two locations; both on the display of the control boxand/or on a display or indicator contained in the patient drive blockcomponent. The block may alternatively include or contain the coil-drivecontroller that facilitates driving single coils, pairs of coils,triplets of coils, quadruplets of coils, or sets of five or more coilstogether. In one implementation of a triplet of coils, in which a pairof coils are driven, the paired driving allows x-y, x-z, or y-z coils ina corner, i.e., in any particular set 106 of coils, to be energized atthe same frequency and same power creating a virtual drive axis at a45-degree angle between the axis pairs. The coil-drive may also have anadditional control to invert the drive waveform (shift the phase 180degrees). This inversion of one coil in the pair may create a virtualdrive axis at −45 degrees, thus creating an orthogonal pair of virtualaxes within a plane. For example, the virtual x-y and x-(−y) are in thesame plane as the x and y axes but rotated 45 degrees within the plane.This paired drive scheme may assist in improving the measurementaccuracy of the system, especially when the sensor coil inside thecatheter tip is substantially or exactly perpendicular to a normal coildrive axis. The system controller may sequentially drive/energize eachcoil, then each pair of coils while measuring the sensor coil response.When the sensor coil is nearly perpendicular to a drive axis there issignificantly diminished response; thus, the virtual axis measurementwill provide more accurate data for the position algorithm. Algorithmswithin the controller may be used to select the best data sets—regularx-y-z axis or virtual x-y-z axis, or a combination thereof—to calculatethe sensor/medical device (e.g., catheter tip) location, position and/ororientation. A display may be used to show the catheter tip location asa position track of x-y location plotted over time plus an indicator forthe z-axis, depth of the catheter. In other embodiments, a display maybe used to show the catheter tip location as a position of x-y locationplotted over time plus an indicator for lateral view or “depth” view asa position of y-z location plotted over time. Depth could also beindicated by a variety of methods, as for example by thickening theposition line segment in the plot as z decreases and thinning theposition line segment as z increases. Moreover, the display may beoperably programmed to automatically scale or zoom as the sensor coilapproaches a designated target placement location chosen on the displayby a default computer setting or a user inputted x-y-z location. Inother alternatives, the external control box or the drive block mayprovide an audible response or command concerning the location,position, or orientation of the sensor coil.

The z-axis (depth) may have particular importance in or for determiningthe implanted depth and therefore be important for proper placement ofthe medical device, as for example a catheter. Issues have existed indetermining accurate location of the z-axis. Particularly, calculationsof the z-axis have been difficult because null sensor coil responsevalues appear in sensing the magnetic field when the sensor coil isapproaching a perpendicular orientation to the z-axis drive coils. Onealternative implementation of a system includes a quadruplet of coils ineach corner of the patient drive block (i.e., a quadruplet in each set106 of coils, each set also defining or being in a “corner” of thetriangle, or trilateration disposition established by the patient driveblock) wherein two axes are orthogonally arranged in the z-dimension,referred to as z′-axis and z″-axis. In this system a pair of coils aredriven, the paired driving allows x-y, x-z′, x′-z″, y-z′, y-z″, andz′-z″ coils in a corner (or respective set 24) to be energized at thesame frequency and same power creating a virtual drive axis at an anglebetween the axis pairs.

It is possible to extend this system further using programmable currentcontrol to the coil-driver circuit. Here, a virtual axis could becreated at any angle between a drive coil pair in a corner (orrespective set 106) by energizing two electromagnetic coils at the samefrequency but with different current drive (power levels to yield avector-sum virtual axis at any angle between 0 and 90 degrees andinverting one coil in this drive scheme to yield a vector-sum virtualaxis at any angle between 0 and −90 degrees). However, an orthogonal setof axes would typically still be selected to accurately locate thesensor coil. A further extension to this system could include energizingall three electromagnetic coils, x-y-z, together in a corner using theprogrammable current controls and inversion controls. The result herewould be a vector sum from x-drive, y-drive, and z-drive coils thatcreates a virtual drive at any vector within three-dimensional space.Alternatively, the system could include energizing all four coils,x-y-z′-z″, together in a corner using the programmable current controlsand inversion controls. In alternatives that include four coils in acorner (or set 106), the result would be a vector sum from the x-drive,y-drive, z′-drive, and z″ drive coils that creates a virtual drive atany vector within three-dimensional space from these coils.

It is also possible to enhance this system with the inclusion ofelectrocardiogram (ECG) measurement and display with the locationsystem. Here two, or more reference electrodes may be plugged into orotherwise connected to the display unit or patient block with theadditional electrode connected to the stylet or guide wire or catheter.An ECG may then be displayed for the user, so that P-wave changes, orother waveform changes may be shown to indicate proximity of the styletor guide wire or catheter to the heart.

An aspect of the present developments is an electromagnetic medicaldevice locating system for locating a medical device or the end or thetip thereof in a subject, including one or more of:

-   -   three or more triplet drive coil sets, each drive coil set        including at least three orthogonally arranged discrete drive        coils, each of the discrete drive coils being electromagnetic        (EM) coils;    -   at least one moveable sensor coil;    -   one or more system components that one or both provide drive        signals energizing said discrete drive coils and measure        resulting sensor coil response signals; wherein the provision of        drive signals includes one or both:        -   (i) sequentially driving one or pairs of said discrete drive            coils within a triplet drive coil set; and        -   (ii) selectively providing phase inversion of the drive            signal to any one or pairs of said discrete drive coils            within a triplet drive coil set;    -   a computing component for calculating sensor coil disposition in        the subject relative to said triplet drive coil sets from one or        more measured resulting sensor coil response signals.

Another aspect of the present developments may be inclusion of a digitalsignal processor operably configured to modify said AC drive frequencyto one or both maximize and optimize the output from the discrete drivecoils. Additionally, the system may include a demodulator forselectively measuring said sensor coil response signal. The demodulatorfurther processes the sensor coil signal and controls a demodulatorclock that operates at the same frequency as the coil AC drive signalwith a phase offset. The digital signal processor controls thedemodulator clock to one or both maximize and optimize the drive coilsthus one or both maximizing and optimizing the sensor coil responsesignal. Further, the digital signal processor may be connected tonon-volatile memory capable of storing: data necessary for controllingthe coil clock frequency data for input to the array of drive coils anddata for controlling the frequency and phase data for the demodulatorclock.

Another aspect may include: (a) three or more virtual or actual x-y-zaxis electromagnetic (EM) triplet drive coils, each including at leastthree virtual or actual EM drive coils arranged in perpendicular axis toeach other along an x-y-z axis, the virtual or actual EM triplet drivecoils placed in a two- or three-dimensional geometric array; (b) atleast one medical device sensor coil in physical association with atleast one medical device tip and connected to at least one demodulatorcircuit; (c) at least one AC drive controller that (i) drivessequentially one or more of the virtual or actual EM drive coils; and(ii) provides a phase shifted signal to the demodulator; (d) at leastone demodulator circuit including at least one demodulator for measuringthe sensor coil output signal using frequency correlation with at leastone AC coil driver signal from the AC drive controller to provide asynchronously demodulated sensor coil signal; (e) at least one automaticgain control circuit that maximizes the demodulated sensor coil signal;(f) a computing component for normalizing the resultant demodulatedsensor coil signal data by dividing or multiplying the determinedprogrammable gain value from the measurement of the demodulated sensorcoil signals; (g) a computing component for selecting and calculatingthe optimized demodulated sensor coil signal data set generated fromdemodulated sensor coil signals, which optimized coil signal data set iscalculated based on the sum of measured squared terms that haverelatively higher or highest values; (h) a calculator for calculatingthe distance of the moveable sensor coil and medical device tip fromthree or more virtual or actual EM triplet drive coil locations usingthe optimized demodulated sensor coil data set calculated usingintersection of the spheres to provide the location of the sensor coiland corresponding medical device tip in space relative to the locationof two or more of the virtual or actual EM triple drive coils providedin the two- or three-dimensional geometric array corresponding to thelocation of the medical device tip in the subject; and in someimplementations, (i) a display. The result is the actual location of themedical device tip in the subject indicating height, width, and depth ofthe medical device tip in the subject calculated relative to theposition of the drive coil geometric array.

It is possible to extend this system to include one or more of (i) thevirtual or actual EM drive coils or the virtual or actual EM tripletdrive coils are arranged outside at least one of a two dimensional planedefined by at least three of the virtual or actual EM triplet drivecoils; and/or (ii) at least four of the virtual or actual EM tripletdrive coils form a tetrahedron as part of the three-dimensionalgeometric array.

It is possible to enhance such a system to include one or more ofwherein (i) the display shows the relative location of the sensor coilor the medical device tip as a tracking of the sensor coil or medicaldevice tip location over time; (ii) the display displays the sensor tipangle graphically for the user of the system, wherein the medical devicetip angle is the angle of maximum response of the sensor coil asmeasured from sweeping the virtual drive axis through x-y plane (e.g. 0to 360 degrees) then using this x-y maximum response angle as a vectoradded to the sweep through the virtual z axis; and/or (iii) the displaydisplays the sensor tip angle graphically for the user of the system,wherein the medical device tip angle is the angle perpendicular to theangle of minimum response of the sensor coil as measured from sweepingthe virtual drive axis through x-y plane (e.g. 0 to 360 degrees) thenusing this x-y minimum response angle as a vector added to sweep throughthe virtual z axis.

It is possible to extend such a system to further include wherein theintensity or power of current running through one or more adjacent EMdrive coils in at least one of the EM triplet drive coils isprogrammable or adjustable using a control box including a programmablecomputer.

An aspect of the present developments is to provide a system wherein oneor more of the EM drive coils are provided as the virtual EM drivecoils, and wherein: (a) one or more controllers that select pairs ortriplets of drive current values of the EM drive coils at regular timeintervals to provide one or more paired magnetic drive coil vectorvalues at angles from 0 to 90 degrees and phase inversion of at leastone of the corresponding EM drive coils in at least one pair of thepaired or tripled magnetic drive coil vectors to further provide one ormore magnetic drive coil vector values at angles from −90 to 0 degrees;(b) one or more controllers that: (i) determine the angle values ofmaximum and minimum sensor coil responses within a plane using pairedcoil programmable current drive sweeping a range from 0 to 90 degrees;and (ii) that then determine the angle values of maximum and minimumsensor coil responses within a plane using paired coil programmablecurrent drive sweeping using inverted phases of at least one coil andsweeping a range from −90 to 0 degrees; and/or (c) a calculator that:(i) computes at least one set of optimal virtual drive x and y axes forat least two of the EM triplet drive coils as values corresponding toplus and minus 45 degrees from the maximum and minimum sensor coilresponses; and (ii) computes an optimal virtual drive z axis orthogonalto the plane of the optimal virtual drive x and y axes to provide atleast one optimal virtual EM triplet drive axes and at least one of thevirtual EM triplet drive coils. This aspect can be further extended tosystems that utilize a quadruplet of drive coils.

Such a system may be extended wherein the system includes a programmablecoil drive current for each of x, y, and z drive coils driven; andwherein (a) the triplets of drive current values selected at regulartime intervals are provided as (i) paired magnetic drive coil vectorvalues at angles from 0 to 90 degrees in an x-y plane together with 0 to90 degrees from the x-y plane to the corresponding z-axis; and (ii) asphase inversion of one or two paired magnetic drive coil vector valuesat angles from −90 to 0 degrees in an x-y plane together with from −90to 0 degrees from the x-y plane to the corresponding z-axis; (b) theangle values of maximum sensor coil responses within a plane for both 0to 90 and −90 to 0 degrees are fixed and used for at least two x and yvirtual axes in a virtual plane and the values of maximum sensor coilresponse are determined for the corresponding virtual z axis to provideat least one maximum virtual x-y-z vector for at least one of thecorresponding virtual EM triplet drive coils; (c) the angle values ofminimum sensor coil responses within a plane for both 0 to 90 and −90 to0 degrees are fixed and used for at least two x and y virtual axes in avirtual plane and the values of maximum sensor coil response aredetermined for the corresponding virtual z axis to provide at least oneminimum virtual x-y-z vector for at least one of the correspondingvirtual EM triplet drive coils; (d) the at least one optimal virtual EMtriplet drive vector and at least one of the virtual EM triplet drivecoils are generated using intermediate virtual drive x and y axes asplus and minus 45 degrees from the minimum virtual x-y-z vector andintermediate virtual drive z axis as orthogonal to the intermediatevirtual drive x and y axis; the optimal virtual x, y, and z axis arethen generated by pivoting the intermediate x, y, and z axes by movingthe intermediate z axis 45 degrees about the maximum virtual x-y-zvector. This aspect can be further extended to systems that utilize aquadruplet of drive coils.

Such a system may be enhanced wherein the display further displaysP-wave or other cardiac waveform changes over time in combination withthe location of the medical device such as a guide wire or stylet tip inrelationship to the subject's heart.

Such a system may be extended by further including (i) an x-axis tiltmeter and y-axis tilt meter which uses gravity to measure the x-axis andy-axis tilt from true vertical; and (2) a computer to calculate anddisplay the location of the medical device tip as height, width, anddepth of the sensor coil corrected for the tilt the geometric array.Such a system may be enhanced wherein the geometric array and sensorcoil connected to the display via a wireless interface.

Such system may be extended by further including an electrocardiogram(ECG) operably associated with the geometric array with a display toshow the subject's ECG signal over time; or by further including anelectroencephalogram (EEG) operably associated with the geometric arraywith a display to show the subject's EEG signal over time. The systemcould be further extended wherein the two or more of the ECH leads areoperably connected to the system via a wireless connection.

An aspect of the present developments may include a method for locatinga medical device in a subject, including: (a) providing a system aspresented herein; (b) inserting and positioning the medical device tipassociated with a functional and sterile medical device into thesubject; and (c) recording or monitoring the output of the display tolocate the medical device tip in the subject. Such a method may beextended wherein the method further includes the use of at least oneselected an electrocardiogram (ECG), an electroencephalogram (EEG), anx-ray machine, an computer assisted tomography (CAT) machine, a positronemission tomography (PET) machine, an endoscope, or an ultrasoundimaging device or composition.

An aspect of the present development may include a system operablyconnected to a ultrasound imaging device. The ultrasound imaging deviceis operably connected to the control box providing a display of thevasculature of the subject. The ultrasound imaging device may be furtherconnected to guidewires, stylets, or catheters that includebiocompatible radiopaque markings at distances, lengths, ormeasurements, that span the circumference or a portion thereof of theguidewire, stylet, or catheter (e.g. inserted component), from theproximal to distal end of the inserted component.

An aspect of the present developments may include methods, computersystems and software, provided as programming code or instructions oncomputer readable media or hardware or networks or computer systems, forgenerating virtual electromagnetic (EM) triplet drive coils forgenerating data corresponding to the location coordinates for a sensorcoil, including:

-   -   (a) electronically providing triplets of drive current values        generated from at least three EM drive coils of the EM triplet        drive coils in detectable proximity to the EM sensor at regular        time intervals to provide one or more paired magnetic drive coil        vector values generated at angles from 0 to 90 degrees without        and from −90 to 0 degrees with phase inversion;    -   (b) electronically providing angle values of maximum or minimum        EM sensor coil responses generated from the EM triplet drive        coils within the x-y plane using paired x-y coils' programmable        current drive sweeping a range from 0 to 90 degrees without and        from −90 to 0 degrees with phase inversion;    -   (c) electronically computing at least one set of optimal virtual        drive x and y axes as values corresponding to plus and minus 45        degrees from the maximum or the minimum sensor coil response;    -   (d) electronically computing an optimal virtual drive z axis        orthogonal to the plane of the optimal virtual drive x and y        axes to provide at least one optimal set of virtual EM triplet        drive axes for at least one of the EM triplet drive coils.

Such a method may be extended wherein (a) the triplets of drive currentvalues selected at regular time intervals are provided as (i) pairedmagnetic drive coil vector values at angles from 0 to 90 degrees in anx-y plane added together with coil vectors of the z-axis from 0 to 90degrees from the x-y plane; and (ii) as phase inversion of one or morepaired magnetic drive coil vector values at angles from −90 to 0 degreesin an x-y plane added together with coil vectors of the z-axis from −90to 0 degrees from the x-y plane; (b) the angle value of maximum sensorcoil response within the x-y plane for both 0 to 90 and −90 to 0 degreesis determined as the intermediate virtual maximum x-y axis and thisintermediate virtual maximum x-y axis added to the z-axis swept from 0to 90 and −90 to 0 degrees to determine at least one maximum virtualx-y-z vector for at least one of the corresponding EM triplet drivecoils; (c) the angle value of minimum sensor coil response within thex-y plane for both 0 to 90 and −90 to 0 degrees is determined as theintermediate virtual minimum x-y axis, and this intermediate virtualminimum x-y axis is added to the z-axis swept from 0 to 90 and −90 to 0degrees to determine at least one minimum virtual x-y-z vector for atleast one of the corresponding EM triplet drive coils; and (d) the atleast one optimal virtual EM triplet drive axes for at least one of theEM triplet drive coils are calculated using the plane defined by themaximum virtual x-y-z vector and minimum x-y-z vector wherein theoptimal virtual drive x and y axes are plus and minus 45 degrees fromthe minimum virtual x-y-z vector and the optimal virtual drive z axis asorthogonal to the optimal virtual drive x and y axes.

FIG. 1 is an overview schematic diagram of an implementation of thepresent developments. A control box 102 contains a touch screen display104 with a computer control and data processing. The triangular patientdrive block 122 is connected via power and communications cable 108 tothe control box 102. The drive and sensor electronics 110 may be locatedin the block 122 and provide drive coil control and sensor coildemodulation/amplification. In the three corners of the block 122 aremounted each triplet drive coil set 106 (106 a, 106 b, 106 c).Alternatively, each coil set 106 could be mounted as feet protrudingfrom the bottom of the block 122. The sensor coil 114 is built onto asmall diameter biocompatible cable 118 which may be inserted into amedical device such as a catheter to be placed in the patient. Thesensor signal is connected back to the control box 102 with a two-wirecable 120. FIG. 7 provides a detailed view of a sensor coil 114. Sensorcoil performance may be improved by winding the coil about aferromagnetic wire in the tip of the cable 138. The ferromagneticmaterial should be used for the length of the sensor coil 114 and may befollowed by non-ferrous material. Two fine wires 142 from the sensorcoil 114 are attached or associated (e.g., glued, wrapped, insulated,and or sheathed) and sealed 140 down the length of the ferrous core wire138.

As presented, e.g., in FIG. 18, an aspect of this device may includecontinuous display at the position of the sensor coil 114 placed in thetip of a medical device as the medical device moves through thepatient's tissue. The patient drive block 122 is placed over thepatient's body where the medical device will be targeted (e.g., over thechest preferably aligned with the sternal notch if the medical devicewill be placed in the area of the heart).

As presented, e.g., in FIGS. 1, 16, 17, and 18, respectively, the sensorcoil cable 120 and patient drive block cable 108 are connected to a usercontrol box 102. The user control box 102 contains a computer 156 (FIG.10) which sequentially drives each driver coil 126, 128, 124 (FIG. 2) oneach axis in every corner 106 a, 106 b, 106 c of the patient drive block122, 150. The coil driver creates magnetic drive vectors as shown inFIG. 9, 10, or 11—where FIG. 9 represents normal drive and FIGS. 10 and11 represent virtual drive. The single board computer 166 (FIG. 21)measures the demodulated output signal from the sensor coil 114 for eachsequentially driven coil set 106 (FIG. 1). The single board computer 156(FIGS. 16 and 21) continuously adjusts the gain of each output signalusing a programmable gain stage in the demodulator electronics andscales all the sensor data to be gain normalized (see FIG. 25b, 25c ,inter alia). Here, gain normalized means that if a measured response isvalue “a” collected at a programmable gain of “4.00” times, then thenormalized resultant value is “a” divided by 4.00. A non-limitingexample of an alternative gain normalizing method is to multiply eachvalue “a” by 4096/gain, e.g. “a”×4096/4.00. The programmable gains thatmay be used as a non-limiting example are 1.00, 2.00, 4.00, 8.00, 16.00and 32.00 plus there may be a final gain stage that is selectable for1.00 or 1.41 (equivalent to 1N2). Examples of a resultant set ofprogrammable gains are 1.00, 1.41, 2.00, 2.82, 4.00, 5.64, 8.00, 11.28,16.00, 22.56 and 32.00.

From the normalized response data, the single board computer 156 (FIG.21) compares the sum of the squares of the sensor's normal response tothe sum of the squares of the sensor's virtual response. Whichever sumis greater or has the stronger response may be used by the computer 156to calculate the sensor coil 114 location using trilateration which isthe calculation of the intersection of three spheres where each sphereis defined as the radial distance of the sensor coil 114 from each x-y-zdriver coil set 106 a, 106 b, 106 c (FIG. 1).

From each corner, the radial distance can be defined as a constantdivided by the 6^(th) root of the sum of the squares of the x, y, and zmeasured normalized response. Here the constant, k, is a calibrationconstant reflecting the strength of each drive coil 124, 126, 128 (FIG.2) and the sensitivity of the sensor coil 114 (FIG. 1). In one possibleaspect, a calibration constant could be generated during manufacturingfor each of the drive coils and then stored as calibration constants foreach coil in non-volatile memory of the patient drive block. Bytrilateration, the radial distance equation for each corner is:

r=k/ ⁶√((x ² y ² +z ²))

The sensor coil location is then calculated from three equations for thethree corners of plate 122:

r ₁ ² =k ²/³√((x ₁ ² +y ₁ ² +z ₁ ²))

r ₂ ² =k ²/³√((x ₂ −d)² +y ₂ ² +z ₂ ²)

r ₃ ² =k ²/³√(x ₃ ²+(y ₃ −d)² +z ₃ ²)

Here d is the distance of each coil from the other and k is thecalibration constant which scales the result into meaningful units ofdistance, e.g. centimeters or inches. In this non-limiting example, thecoils on the patient drive plate or block 122 (FIGS. 1, 16, 17 interalia) are arranged in a right triangle, with two sides of equal length,d, as reflected in the 2^(nd) and 3^(rd) equations above, just ondifferent axis, x or y. The solution to these equations yielding thesensor coil location is:

x _(s)=(r ₁ ² −r ₂ ² +d ²)/2d

y _(s)=(r ₁ ² −r ₃ ² +d ²)/2d

z _(s)=+/−²√(r ₁ ² −x _(s) ² −y _(s) ²)

Here the solution for z (vertical axis) is assumed to be negative as thesensor coil 114 cannot be above the plane of the patient drive block 122(FIGS. 1, 16, 17, 18, 19 inter alia) unless it is outside the patient.

While the above reflects one non-limiting approach to locating thesensor coil 114 (FIG. 1), it is not the only solution for coil location.Specifically when the sensor coil 114 is nearly perpendicular to adriver coil axis the sensor coil response approaches zero; therefore a“virtual axis” drive system, in some instances, provides for the optimalsensor coil response. In this approach the coil driver circuit isdesigned to selectively drive, within a triplet set, pairs of coils,e.g. 124 and 126 (FIG. 2), together at the same frequency and amplitudewith an additional driver control to selectively invert the phase of onecoil in the pair. This paired coil drive of x-y coils creates the 1stvirtual axis at forty-five degrees from the original x and y axes. Thepaired coil drive is then operated with x-(−y) which drives the x-coiltogether with inverted-phase y-coil and this creates the 2^(nd) virtualaxis at minus forty-five degrees from the original x and y axes. Theresult is two orthogonal virtual magnetic vectors as shown by the dashedlines in FIG. 9 for x-y paired coil drive or in FIG. 10 for y-z pairedcoil drive. For paired drive, the single board computer 156 (FIG. 16)sequentially drives the x-y pair, x-(−y) pair, and z axis for each x-y-zcoil set 106 a, 106 b, 106 c (FIGS. 1 and 7). Here, “(−y)” meansinverted phase on y axis drive. The measured sensor coil response forpaired-coil drive must be scaled down by √2 or 1.4142 because of vectorsumming of the two coils driven together. Alternatively, the coil-driverpower could be scaled down by 1/√2 or 0.7071 in hardware when drivingpairs so that the vector sum of two coils equals the magnetic vector ofa single coil drive. The single board computer 156 measures the sensorcoil response for each corner in normal drive and paired drive, and thenselects the strongest signal from each corner comparing the sum of x²,y², and z² normal coil drive response to the sum of (x-y)², (x-(−y))²,and z² paired coil drive response. The strongest signal from each corneris used to calculate the location of the sensor coil 114 using thetrilateration method described in the above equations. This exampleillustrates paired x-y coil drive; and by logical extension this mayalso apply to x-z, or y-z paired drive. An objective in someimplementations of these developments may include improving the accuracyof horizontal (x-y) location; therefore the paired x-y drive can bepreferred over x-z or y-z.

In an alternative embodiment and/or method, the single board computer156 (FIG. 21) uses the normalized response data to compare the sum ofthe squares of the sensor's normal response to the sum of the squares ofthe sensor's virtual response. Whichever sum is greater or has thestronger response may be used by the computer 156 to calculate thesensor coil 114 location using trilateration which is the calculation ofthe intersection of three spheres where each sphere is defined as theradial distance of the sensor coil 114 from each x-y-z driver coil set106 a, 106 b, 106 c (FIG. 1).

In this alternative embodiment, from each corner, the radial distancemay be defined as a constant divided by the 6^(th) root of the sum ofthe squares of the x, y, and z measured normalized response. Here theconstant, k, is a calibration constant reflecting the strength of eachdrive coil 124, 126, 128 (FIG. 2) and the sensitivity of the sensor coil114 (FIG. 1). In one possible approach, a calibration constant could begenerated during manufacturing for each of the drive coils and thenstored as calibration constants for each coil in non-volatile memory ofthe patient drive block. By trilateration, the radial distance equationfor each corner is:

r=k/ ⁶√((x ² +y ² +z ²))

In this approach for calculation of the EM tip location, bytrilateration, the sense coil location [x, y, z] distance equation foreach corner is:

xs=(r ₁ ² −r ₂ ² +d ²)/(2d)

ys=[(r ₁ ² −r ₃ ² +i ² +j ²)/(2j)]−[(i/j)·xs]

zs=+/−√[r ₁ ² −xs ² −ys ²]

In this alternative, the coordinates of the sphere used fortrilateration may be as follows: sphere 1=[0,0], sphere 2=[0,d], andsphere 3=[i,j]. One should note that there are two solutions to the zsanswer, in this instance, the “+” and the “−” solution. The computercomponent is operably programmed to select the solution for the negativeanswer as the assumption is made that the sensor coil 114 cannot beabove the plane of the patient drive block unless it is outside thepatient. In this alternative, by trilateration, the radial distanceequation for each corner is:

r ₁ ² =k/ ⁶√((mx ₁ ² +my ₁ ² +mz ₁ ²))

r ₂ ² =k/ ⁶√((mx ₂ ² +my ₂ ² +mz ₂ ²))

r ₃ ² =k/ ⁶√((mx ₃ ² +my ₃ ² +mz ₃ ²))

In this alternative, mx₁, my₁, and mz₁ are measured sense coil responsesfrom corner 1 124; mx₂, my₂, and mz₂ are measured sense coil responsesform corner 2 126; and mx₃, my₃, and mz₃ are measured sense coilresponses from corner 3 128. Furthermore, a non-limiting approach may beimplemented when the sensed or measured z-signal is approaching a nullor alternatively when the measuring or determining component determinesthat a null signal was received. Here, the z-signal is estimated usingthe following:

mz ²=((mx ² +my ²)×(1/√2));

or,

mz ²=((mx ² +my ²)×(0.7071))

In this alternative, the location of the sense coil is calculated usingthe vector sums of x and y to estimate the z vector; thus, preventingthe return of a null signal. In this alternative, due to the drive coilfields and due to location and spacing of the drive coils, the nulls ofone corner do not overlap the nulls of another corner.

The sensor coil location is then calculated from three equations for thethree corners of plate 122, in this instance substituting the aboveestimated z-signal in the place of the z vector, to:

r ₁ ² =k/ ⁶√((mx ₁ ² +my ₁ ²+((mx ₁ ² +my ₁ ²)×(1/√2))

r ₂ ² =k/ ⁶√((mx ₂ ² +my ₂ ²+((mx ₂ ² +my ₂ ²)×(1/√2))

r ₃ ² =k/ ⁶√((mx ₃ ² +my ₃ ²+((mx ₃ ² +my ₃ ²)×(1/√2))

The solution to these equations yielding the sensor coil location is:

x _(s)=(r ₁ ² −r ₂ ² +d ²)/2d

y _(s)=(r ₁ ² −r ₃ ² +d ²)/2d

z _(s)=+/−²√(r ₁ ² −x _(s) ² −y _(s) ²)

Here the solution for z (vertical axis) is assumed to be negative as thesensor coil 114 cannot be above the plane of the patient drive block122, 150 (FIGS. 1, 16, 17, 18 inter alia) unless it is outside thepatient.

While the above reflects one non-limiting approach to locating thesensor coil 114 (FIG. 1), it is not the only solution for coil location.Specifically when the sensor coil 114 is nearly perpendicular to adriver coil axis the sensor coil response approaches zero; therefore a“virtual axis” drive system provides for an additional sensor coilresponse. In this approach the coil driver circuit is designed toselectively drive, within a triplet set, pairs of coils, e.g. 126 and124 (FIG. 2), together at the same frequency and amplitude with anadditional driver control to selectively invert the phase of one coil inthe pair. This paired coil drive of x-y coils creates the 1st virtualaxis at forty-five degrees from the original x and y axes. The pairedcoil drive is then operated with x-(−y) which drives the x-coil togetherwith inverted-phase y-coil and this creates the second virtual axis atminus forty-five degrees from the original x and y axes. The result istwo orthogonal virtual magnetic vectors as shown by the dashed lines inFIG. 9 for x-y paired coil drive or in FIG. 10 for y-z paired coildrive. For paired drive, the single board computer 156 (FIG. 21)sequentially drives the x-y pair, x-(−y) pair, and z axis for each x-y-zcoil set 106 a, 106 b, 106 c (FIGS. 1 and 15). Here, “(−y)” meansinverted phase on y axis drive. The measured sensor coil response forpaired-coil drive must be scaled down by 1.4142 because of vectorsumming of the two coils driven together. Alternatively, the coil-driverpower could be scaled down by 0.7071 in hardware when driving pairs sothat the vector sum of two coils equals the magnetic vector of a singlecoil drive. The single board computer 156 measures the sensor coilresponse for each corner in normal drive and paired drive, and thenselects the strongest signal from each corner comparing the sum of x²,y², and z² normal coil drive response to the sum of (x−y)², (x-(−y))²,and z² paired coil drive response. The strongest signal from each corneris used to calculate the location of the sensor coil 114 using thetrilateration method described in the above equations, using theimproved method. This example illustrates paired x-y coil drive; and bylogical extension this may also apply to x-z, or y-z paired drive, or inalternative structures orthogonal pairs of drive coils.

In a non-limiting approach, the z-axis coil is replaced by a pair oforthogonal coils, z′ and z″ (FIGS. 4, 5, 6, 12, 13, and 14 inter alia).These z′ and z″ coils are arranged in pseudo-orthogonal or dualorthogonal placement. In this approach, the z-coil responses or measuredz-coil values are calculated as the vector sum of the sense coilsresponse to z′ and z″. By trilateration, the radial distance equationfor each corner is:

r=k/ ⁶√((z′ ² +z″ ² +a ²))

where “a” is calculated using the x-y sense coil measurementinformation, then here, the location of the sense coil [z′, z″, a] wouldbe:

r ₁ ² =k/ ⁶√((mz′ ₁ ² +mz″ ₁ ² +ma ₁ ²))

r ₂ ² =k/ ⁶√((mz′ ₂ ² +mz″ ₂ ² +ma ₂ ²))

r ₃ ² =k/ ⁶√((mz′ ₃ ² +mz″ ₃ ² +ma ₃ ²))

In this alternative, mz′₁, mz″₁, and ma₁ are measured sense coilresponses from corner 1 124; mz′₂, mz″₂, and ma₂ are measured sense coilresponses form corner 2 126; and mz′₃, mz″₃, and ma₃ are measured sensecoil responses from corner 3 128. In this alternative, ma₁ ², ma₂ ², andma₃ ² are measured vectors using the x drive coil and y drive coil toobtain the vector sum for each corner. In this alternative method forcalculation of the EM tip location the, by trilateration, the sense coillocation [z′, z″, and a] distance equation for each corner is:

z′=(r ₁ ² −r ₂ ² +u ²)/(2u)

z″=[(r ₁ ² −r ₃ ² +v ² +w ²)/(2×w)]−[(v/w)×a]

a=+/−√[r ₁ ² −z′ ² −z″ ²]

In this alternative, the coordinates of the sphere used fortrilateration may be as follows: sphere 1=[0,0], sphere 2=[0,u], andsphere 3=[v,w]. This or alternative sets or combinations of the abovenon-limiting approaches may be utilized within the system.

An improvement of the paired-coil drive may be to add programmable (DAC)power control to the coil drivers on the drive coil drive electronicsboard 110 (FIGS. 22, 23, 28, and 31). Here, the single board computer156 (FIG. 16, 21) has the capability to select pairs of drive currentpower settings which steer the virtual axis of the paired coils from 0to 90 degrees. Inversion of one of the coil drivers in the pair providesthe capability for virtual axis from −90 to 0 degrees. In this design,the single board computer 156 selects pairs of power settings output tothe x-y paired coil driver to sweep the virtual drive axis from 0 to 90degrees while recording the sensor coil response and this process isrepeated with the y-coil driver phase inverted to sweep from −90 to 0degrees. The angle of the virtual axis when the sensor coil responsedata is maximum indicates the sensor coil 114 (FIG. 1) is parallel tothe virtual axis and the angle of the virtual axis when the sensor coilresponse data is minimum indicates the sensor coil 114 is perpendicularto the virtual axis. Here the maximum angle and minimum angle areorthogonal (perpendicular). The single board computer 156 (FIG. 16, 21)calculates the optimum virtual x axis at forty-five degrees from themeasured angle for maximum (or minimum) response and calculates theoptimum virtual y axis as an angle orthogonal to the virtual x axis. Asall x-y-z coil sets 106 a, 106 b, 106 c, (or x-y-z′-z″) are mechanicallyaligned the solution for best virtual axes in one corner applies to allcorners in the patient drive block 122, 150 (FIGS. 1, 16, 17 and 18).The single board computer 156 (FIG. 16, 21) measures the sensor coilresponse for all corners using these optimum virtual x axis, optimumvirtual y axis plus normal z axis. The sum of (virtual x)², (virtualy)², and z² sensor coil responses for each corner is used to calculatethe position of the sensor coil 114 (FIG. 1) using the trilaterationmethod described in the above equations. This example illustrates pairedx-y coil drive; and by logical extension this also applies to x-z, ory-z paired drive; however, the preference in this development is toimprove accuracy of horizontal location and thus use paired x-y drive.Furthermore, in arrangements that utilize a quadruplet embodiment ofdrive coils, the single board computer 156 (FIG. 16) may calculate thesensor coil location for all corners using an optimized choice of themeasured x, virtual x, measured y, virtual y, virtual x-y, measured z′,virtual z′, measured z″, virtual z″, and virtual z′-z″.

An alternative, non-limiting, method for finding the optimum virtual xand virtual y axis in the programmable pair-coil drive above is to usesuccessive approximation instead of sweeping 0 to 90 degrees. In thisapproach, the single board computer 156 (FIG. 16) has the capability toselect pairs of drive current power settings which steer the virtualaxis from −90 to +90 degrees. The single board computer first tests thesensor coil response to the paired coils at virtual axes +45 and −45degrees and selects the virtual axis with the stronger response. Usingthe stronger axis, the computer then tests the sensor coil response topaired coils at +22.5 and −22.5 degrees from the current virtual axisand selects the virtual axis with the stronger response. This processcontinues for +/−11.25 degrees, +/−5.625 degrees, until the limits ofdrive power resolution are reached. The resulting virtual axis is theaxis of maximum response. The single board computer 156 calculates theoptimum virtual x axis at forty-five degrees from the measured angle formaximum response and calculates the optimum virtual y axis as an angleorthogonal to the virtual x axis. This approach may in some embodimentsbe extended to the z′ and z″ drive coils.

A selection of the best set of virtual axes in a triplet-coil drivescheme may be accomplished with programmable power control to the coildrivers for each axis, and with the driver control to selectively invertthe phase of any coil in the triplet x-y-z coil sets 106 a, 106 b, 106 c(see FIG. 16). Here, the single board computer 156 (FIG. 16) has thecapability to select pairs of drive current power settings which steerthe x-y virtual axis of the paired coils from 0 to 90 degrees. Inversionof one of the coil drivers in the pair provides the capability forx-(−y) virtual axis from −90 to 0 degrees. With the addition of thethird coil drive and inversion the single board computer 156 may sweepthe virtual axis 0 to 90 and −90 to 0 degrees in z range. Themicrocomputer (in alternative embodiments multiple microcomputers) mayselect the pairs of current settings output to the x-y paired coildriver to sweep the virtual drive axis from 0 to 90 degrees whilerecording the sensor coil response and this process is repeated with they coil driver phase inverted to sweep from −90 to 0 degrees. The angleof the x-y virtual axis when the sensor coil response data is maximumindicates the sensor coil 114 (FIG. 1, 16) is parallel for the x-yplane. The single board computer 156 then sets this x-y axis and sweepsthe z axis drive from −90 to 0 and 0 to 90 degrees while recording thesensor coil response. The polar angle of the x-y-z virtual axis when thesensor coil response data is at maximum indicates the sensor coil 114 isparallel to this virtual x-y-z axis. The single board computer 156 thenrepeats this process to find the minimum sensor coil response sweepingx, y, and z axes. The polar angle of the x-y-z virtual axis when thesensor coil response data is minimum indicates the sensor coil 114 isperpendicular to this virtual x-y-z axis. These two vectors, virtualminimum and virtual maximum, define a plane intersecting the sensor coil114. For optimum response, the single board computer 156 calculates avirtual x axis 45 degrees between the maximum and minimum vectors, thencalculates the virtual y axis as 90 degrees from the virtual x in theplane defined previously. Here, virtual z axis is defined as orthogonalto the plane of virtual minimum and virtual maximum vectors. The singleboard computer 156 then tilts the virtual z axis and the plane ofvirtual x axis and virtual y axis 45 degrees toward the virtual minimumvector, and the result is the optimal virtual axis set which maximizesthe sensor coil response. As all x-y-z coil sets 106 a, 106 b, 106 c aremechanically aligned the solution for best virtual axes in one cornerapplies to all corners in the driver array. The single board computer156 measures the sensor coil response for all corners using theseoptimum virtual x, y, and z axes. The sum of (virtual x)², (virtual y)²,and (virtual z)² sensor coil responses for each corner may be used tocalculate the sensor coil 114 location and orientation using thetrilateration method described in the above equations. One method tomaintain the optimum x-y-z axis over time is to continuously test thesensor coil response to small deviations (offset angle) from the optimumaxis (see FIG. 29b ). Here, the single board computer 156 compares thesum of (virtual x)², (virtual y)², and (virtual z)² sensor coilresponses for the current virtual axis to the sum for virtual axis plusoffset angle and the sum for virtual axis minus offset angle. Thecomputer 156 then selects the axis with the largest summed response—thisbecomes the new optimum x-y-z axis and the process continues to iteratetesting small deviations over time. This approach may in someembodiments be further extended for use in quadruplet drive coil sets.

The single board computer 156 may then graphically display the sensorcoil position on the display 104 of the control box 102. The position iscontinuously updated adding onto the previous graphical data to create atrack or path of the sensor coil 114 over time. Furthermore, as thetrack or path of the sensor coil 114 is displayed, the display alsoshows the orientation of the sensor coil in at least the x-y coordinateplane. The user interface of the single board computer 156 allows theuser to clear the recorded track or to save the recorded track tonon-volatile memory. Touch-screens have been described; however keyboardor other data input, or user interface options may be used.

The construction details above for the control box 102 (FIGS. 1, 21) mayprovide for a tethered device with the display/control separate from thepatient block 122, 150 (FIGS. 1, and 21). However, an alternativeconstruction would be to build a device or system in which the patientblock 122, 150 is battery-powered and connected wirelessly to thecontrol box 102. In another variation, the control box 102 could beintegrated into or as part of the patient block and placed on thepatient chest or other locations to track medical device position.Wireless and/or wired connections are thus optionally available for theconnections of the drive coil sets to the control or system componentsfor the driving thereof; as well as for the connections of the sensorcoil to the control or system components for measuring or receiving theresponse signals of the sensor coil.

An alternative construction would be to use four or more drive coils 106oriented as a square, rectangle, pentagon, circle, oval, geometric, orany other suitable shape, in or as the patient drive block 122, 150(FIGS. 1, 18, 19 and 20). In this non-limiting approach, the location,disposition, and orientation may be determined using multilateration.

An alternative construction would be to use a capacitor 131 (FIG. 6) inoperable association with each of the discrete drive coils 106 or eachaxis of each discrete drive coil 124, 126, and 128. This alternativeembodiment may create an LC circuit that has unique benefits foroptimizing the energizing of the drive coils, the re-energizing of thedrive coils, the sequential energizing of the drive coils, thesynchronous energizing of the drive coils, and the de-energizing thedrive coils.

An alternative construction (FIG. 1, 16, 17, and/or 18) is to optionallyincorporate electrocardiograph (ECG) monitoring into the medical devicelocation system to facilitate placement of the medical device withsensor coil 114 in close proximity to the heart. Here the patient driveblock 150 may be modified with one or more ECG pads 154 and ECG leadwires 152 which attach to the patient's chest and the third ECG lead isprovided by a conductive wire 146 added in or otherwise made part of thecore of the guide wire or stylet sensor coil 114.

An ECG amplifier may be added to the main interface board 158 (FIG. 22),and the single board computer 156 may then present the ECG on thedisplay 104 as the medical device such as a catheter is advanced withinthe patient's or subject's body. The user may observe changes in theP-wave or other wave elements of the ECG as the medical device/catheterreaches the heart. Ideally, the single board computer 156 could use awaveform analysis to assist the user in recognizing changes occurring tothe P-wave or other waveforms.

A component to this design may include connecting the signals from thesensor coil 114 and ECG 146 to the user control box 102. This iscomplicated in practice by covering the entire patient and patient block150 with sterile drapes for insertion of the patient's medicaldevice/catheter. In this design, a miniature stereo phone plug orsimilar could be used to pierce a plastic bag and connect to cable 120,146 a pigtail from the user control box 102.

Methods, devices and systems may thus be provided for one or both oftwo- or three-dimensional location of the disposition of a sensor coilin a subject including: an array of electromagnetic drive coil sets,each set having two or three dimensionally oriented drive coils; asensor coil being electromagnetically communicative with the array ofelectromagnetic drive coil sets; and, a system controller communicativewith and adapted to energize one or more of the electromagnetic coils inthe array of electromagnetic drive coil sets, the energizing of the oneor more of the electromagnetic coils including one or more of energizingthe coils singly, or in pairs of x-y and y-z or x-z coils or x-y andy-z′ and/or y-z″or x-z′ and/or x-z″and/or z′-z″ coils while measuringthe response of the sensor coil; whereby the system uses themeasurements of the responses of the sensor coil to calculate thelocation and orientation of the sensor coil relative to said drive coilsets.

This may include two- and/or three-dimensional location of a catheter intissue using an array of x-y or x-y-z or x-y-z′-z″ orientedelectromagnetic coils, where a sensor coil may be associated with one ormore catheter tips, and where the system controller may energize one ormore external coils, such as but not limited to, pairs of x-y and y-z orx-z coils or x-y and y-z′ and/or y-z″or x-z′ and/or x-z″ and/orz′-z″coils while measuring the response of the sensor coil; the systemmay use these sensor coil measurements to calculate the position andorientation of the catheter tip, and in some implementations, the systemcontroller may graphically display the catheter tip position, depthand/or orientation, e.g., but not limited to, over time.

From the foregoing, it is readily apparent that new and usefulimplementations of the present systems, apparatuses and/or methods havebeen herein described and illustrated which fulfill numerous desideratain remarkably unexpected fashions. It is, of course, understood thatsuch modifications, alterations and adaptations as may readily occur tothe artisan confronted with this disclosure are intended within thespirit of this disclosure, which is limited only by the scope of theclaims appended hereto.

What is claimed is:
 1. A medical device locating system for determininga disposition of a sensor in a subject, the system comprising: an arrayof three or more quadruplet drive coil sets, each quadruplet drive coilset including at least four discrete drive coils, each of the discretedrive coils being electromagnetic coils; at least one moveable sensorcoil configured to provide one or more sensor coil response signals; afirst system component providing AC drive signals to energize thediscrete drive coils, wherein the first system component is configuredto provide the AC drive signals by: sequentially driving one or more ofthe discrete drive coils within each quadruplet drive coil set; orselectively providing phase inversion of the drive signal to any one ormore of the discrete drive coils within each quadruplet drive coil set;a second system component for receiving the one or more sensor coilresponse signals from the at least one moveable sensor coil; and aprocessor configured to determine a sensor coil disposition of the atleast one moveable sensor coil in the subject relative to the quadrupletdrive coil sets based on the one or more sensor coil response signals.2. The system of claim 1, wherein at least two of the discrete drivecoils in each quadruplet drive coil set are arranged perpendicularlyrelative to each other in one or more of an x-y, x-z, or y-z array, andat least two of the discrete drive coils in the same quadruplet drivecoil set are arranged perpendicularly relative to each other andgeometrically oriented off axis at both a negative 45 degree angle andpositive 45 degree angle away from the respective x, y, or z axis. 3.The system of claim 2, wherein the processor is configured to determinethe sensor coil disposition of the at least one moveable sensor coil inthe subject using an intersection of spheres, wherein the one or moresensor coil response signals from coil pairs oriented plus and minus 45degrees off axis are vector summed to yield one axis of data.
 4. Thesystem of claim 1, further comprising a display configured to displaythe disposition of the at least one moveable sensor coil in the subjectrelative to the quadruplet drive coil sets.
 5. The system of claim 4,wherein the display is configured to display the disposition of the atleast one moveable sensor coil in the subject by displaying one or moreof a height, width or depth of the at least one moveable sensor coil inthe subject relative to the quadruplet drive coil sets.
 6. The system ofclaim 4, wherein the display is configured to display the disposition ofthe at least one moveable sensor coil in the subject by displaying anangular orientation of the at least one moveable sensor coil relative tothe quadruplet drive coil sets.
 7. The system of claim 1, wherein theprocessor is configured to determine the sensor coil disposition of theat least one moveable sensor coil in the subject by: calculating sensorcoil signal data sets generated from the one or more sensor coilresponse signals; selecting optimum sensor coil signal data sets fromthe calculated sensor coil signal data sets based on the magnitude ofthe sensor coil signal data sets; and calculating an intersection ofspheres using the optimum sensor coil signal data sets to determine thesensor coil disposition of the at least one moveable sensor coil in thesubject relative to the quadruplet drive coil sets.
 8. The system ofclaim 1, further comprising one or more electrocardiogram referenceleads placed on the subject and an electrocardiogram lead provided by aconductive core wire supporting the sensor coil.
 9. The system of claim8, further comprising a display configured to display theelectrocardiogram signal of the subject over time.
 10. The system ofclaim 9, wherein the display is further configured to display the P-waveof the subject over time in combination with the disposition of the atleast one moveable sensor coil in the subject relative to the quadrupletdrive coil sets.
 11. The system of claim 1, further comprising one ormore of a catheter, a guide wire or a stylet with the at least onemoveable sensor coil being disposed in a distal portion therewith, andfurther comprising an integrated electrocardiogram lead associated withthe sensor coil, the electrocardiogram lead providing an electricalelectrocardiogram signal.
 12. The system of claim 1, further comprisingan automatic gain control circuit within the first system component orthe second system component, the automatic gain control circuit beingconfigured to maximize the one or more sensor coil response signalsbefore the one or more sensor coil response signals are received by thesecond system component.
 13. The system of claim 1, further comprising auser control box, wherein the array of the three or more quadrupletdrive coil sets and the at least one moveable sensor coil are connectedto the user control box.
 14. The system of claim 1, wherein the firstsystem component is further configured to continually adjust or programthe intensity or power of current through one or more of the discretedrive coils in at least one or more of the quadruplet drive coil sets.15. The system of claim 1, further comprising an x-axis tilt meter andy-axis tilt meter configured to measure the x-axis and y-axis tilt froma true vertical, wherein the processor is further configured tocalculate the disposition of the at least one moveable sensor coil as aheight, width, and depth of the sensor coil corrected for the tilt ofthe array of the array of the three or more quadruplet drive coil sets.16. A medical device locating system for determining a disposition of asensor coil in a subject, the system comprising: an array of three ormore quadruplet drive coil sets, each quadruplet drive coil setincluding at least four discrete drive coils, each of the discrete drivecoils being electromagnetic coils; at least one moveable sensor coilconfigured to provide one or more sensor coil response signals; a firstsystem component providing AC drive signals to energize the discretedrive coils, wherein the first system component is configured to providethe AC drive signals by: simultaneously driving two or more of thediscrete drive coils at two or more different current intensity or powerlevels each quadruplet drive coil set to generate an electromagneticfield defining a virtual axis, or simultaneously driving two or more ofthe discrete drive coils within each quadruplet drive coil set with twoor more drive signals with inversed phase; a second system component forreceiving the one or more sensor coil response signals from the at leastone moveable sensor coil; and a processor configured to determine asensor coil disposition of the at least one moveable sensor coil in thesubject relative to the quadruplet drive coil sets based on the one ormore sensor coil response signals.
 17. The system of claim 16, whereinat least two of the discrete drive coils in each quadruplet drive coilset are arranged perpendicularly relative to each other in one or moreof an x-y, x-z, or y-z array, and at least two of the discrete drivecoils in the same quadruplet drive coil set are arranged perpendicularlyrelative to each other and geometrically oriented off axis at both anegative 45 degree angle and positive 45 degree angle away from therespective x, y, or z axis.
 18. The system of claim 16, furthercomprising a display configured to display the disposition of the atleast one moveable sensor coil in the subject relative to the quadrupletdrive coil sets.
 19. A medical device locating system for determining adisposition of a sensor coil in a subject, the system comprising: anarray of three or more quadruplet drive coil sets, each quadruplet drivecoil set including at least four discrete drive coils, each of thediscrete drive coils being electromagnetic coils; at least one moveablesensor coil configured to provide one or more sensor coil responsesignals; a first system component providing AC drive signals to energizethe discrete drive coils, wherein the first system component isconfigured to provide the AC drive signals by: simultaneously drivingtwo or more of the discrete drive coils at two or more different currentintensity or power levels within each quadruplet drive coil set togenerate an electromagnetic field defining a virtual axis, orsimultaneously driving two or more of the discrete drive coils withineach quadruplet drive coil set with two or more drive signals withinversed phase; a second system component for receiving the one or moresensor coil response signals from the at least one moveable sensor coil;and a processor configured to determine a sensor coil disposition of theat least one moveable sensor coil in the subject relative to thequadruplet drive coil sets based on the one or more sensor coil responsesignals.
 20. The system of claim 19, wherein at least two of thediscrete drive coils in each quadruplet drive coil set are arrangedperpendicularly relative to each other in one or more of an x-y, x-z, ory-z array, and at least two of the discrete drive coils in the samequadruplet drive coil set are arranged perpendicularly relative to eachother and geometrically oriented off axis at both a negative 45 degreeangle and positive 45 degree angle away from the respective x, y, or zaxis.